Abaixo está uma instrução que descreve uma tarefa de geração de SQL, combinada com uma entrada que fornece mais contexto sobre os esquemas de tabela disponíveis. Escreva o código SQL que responda adequadamente à solicitação
 ###Instrução: Quantas equipes têm 21 tentativas para?
 ###Tabelas: CREATE TABLE group_stage (group_stage_id AUTO_INCREMENT PRIMARY KEY, Date VARCHAR, Opponents VARCHAR, Result F–A VARCHAR, Attendance INT, Group position VARCHAR) CREATE TABLE best_figures_in_a_match (best_figures_in_a_match_id AUTO_INCREMENT PRIMARY KEY, Rank VARCHAR, Bowling VARCHAR, Player VARCHAR, Opponent VARCHAR, Venue VARCHAR, Season VARCHAR) CREATE TABLE league_table (league_table_id AUTO_INCREMENT PRIMARY KEY, Club VARCHAR, Played VARCHAR, Won VARCHAR, Drawn VARCHAR, Lost VARCHAR, Points for VARCHAR, Points against VARCHAR, Points difference VARCHAR, Tries For VARCHAR, Tries Against VARCHAR, Try Bonus VARCHAR, Losing Bonus VARCHAR, Points VARCHAR) CREATE TABLE week_7 (week_7_id AUTO_INCREMENT PRIMARY KEY, Couple VARCHAR, Style VARCHAR, Music VARCHAR, Trine Dehli Cleve INT, Tor Fløysvik INT, Karianne Gulliksen INT, Christer Tornell INT, Total INT) CREATE TABLE players_with_100_or_more_appearances (players_with_100_or_more_appearances_id AUTO_INCREMENT PRIMARY KEY, Name VARCHAR, Position VARCHAR, Club career VARCHAR, League apps INT, League goals INT, Total apps INT, Total goals INT)  
SELECT COUNT Points difference FROM league_table WHERE Tries For = 21